Photographic printing emulsion



Patented Mar. 26, 1935 PATENT oFFicE- 1,995,444 PHOTOGRAPHIC PRINTING EMULSION William Ambler Berry,

Edgware, and Bertram Vincent Storr, Ilford, England, assignors to Ilford Limited, Ilford,

ish company Essex, England, a Brit-' ,No Drawing. ApplicationAugust 31, 1932, Serial No. 631,272. In Great Britain September 3,

9 Claims.

This invention comprises improvements in or relating to photographic printing emulsions which may be applied to a paper or any other preferred support, and which contain a silver halide, preferably silver chloride.

It has been found, when silver chloride is used alone as the light-sensitive constituent of the emulsion, that the: print obtained by exposure to light without development is poor in gradation:

and density and that generally a print so obtained has no value.

With a view to overcoming this difiiculty it has been the practice to incorporate in the emulsion-a soluble silver salt, for example, silver citrate. This procedure, however, has the disadvantage that the keeping qualities of the print-- ing paper are poor owing to the fact that the soluble silver salts are easily decomposable.

One object of the present invention is to provide a photographic printing paper which will not suffer from the above liability towards deterioration and which at the'same time, will, on

completion of printing, give images-of good tone.

The invention provides a, print-out photographic emulsion in which the print-out properties are produced by the addition of a soluble manganese saltinstead of a solublesilver salt to an emulsion whereof the silver salt content is substantially insoluble in water, for example co sists exclusively of silver chloride.

- Solubility is of course a comparative term, but salts such as the chloride, bromide and iodide of silver are commonly regarded 'asinsoluble while for example the citrate, sulphate and fluoride are regarded as soluble silver salts. The latter when used in photographic emulsions coated on paper, tend to percolate into the paper base whereas the former salts do not exhibit this tendency; The term substantially insoluble is used in the above sense in this specification.

The emulsion may also contain a" gold salt, preferably together with a lead salt and a thiocyanate, e. g. a thiocyanate of an alkali metal or of ammonium; The addition of the gold salt to the emulsion renders the latter, as is known, selftoning. The addition of the lead salt increases the amount'o-f brilliancy of the toning, while the thiocyanate assists in controlling the quality of tone.

According to a further feature of the invention the emulsion is prepared by the precipitation of silver chloride from a solution of a soluble silver salt (silver nitrate) by the addition of a solution of manganese chloride.

It is to be understood that the term printing paper asused in this specification with reference to the material prepared according to the inventionimplies a paper of the type normally known as a.printing-.out paper, but need not necessarily be employedias such, as it is possible to use the paper by a development method.

Ordinary self-toning printing-out papers'if given aLshort exposure so as to yield a just visible image andthen treated by the ordinary developing and fixing baths do not give satisfactory prints and it is therefore the practice to give them a comparatively long exposure and then to fix the imageso obtained'in sodiumthiosulphate. It is, however, an advantage of the printing paper according to this invention that with a short'exposure followed by development and fixing a satisfactory gold-toned image can be obtained. The invention therefore method. of obtaining an image on paper or other material bearing an emulsion-comprising as aforesaid an insoluble silver salt or salts and a salt of manganese, which consists in givingthe paper an exposure insuflicient for the complete printing-out of the image, and thereafter completing the production of v the image by development. More specifically the method according to the invention may consist in exposing a paper bearing an emulsion comprising an insoluble silver salt or salts, a salt of manganese and. a

gold salt (with or without a lead-salt and/or a thiocyanate), developing the exposed paper in a solution to produce a reddish image, and finally toning and fixing theprint, for example by immersion in a solution of sodium thiosulphate, preferably containing a thiocyanate of an alkali metal or of ammonium. During the immersion in a thiosulphate bath the colour of the print changesrgradually from red-through sepia to a warm black. It will be understood that any desired tone within certain limits may be obtained in'the' print, by continuing the treatment in the toning and fixing bath until the correct shade of colour-has been reached and then withdrawing the print from the bath and washing thoroughly.

An example of the manufacture of an emulsion according to this invention will now be described. A solution comprising gelatin, water, citric acid and silver nitrate was. made up at F. and to this was added a solution of manganese chloride in quantity more than sufiicient to precipitate all the silver in the form of silver chloride. A solution of gold thiocyanate was prepared by the addition to a solution of gum arabic of gold chloride and ammonium thiocyanate, and this was then mixed with the gela includes a Gelatin Water 200 ccs. 2 /2N silver nitrate 10.0 ccs. 25% gold chloride (NaAuCl-l) 0.75 ccs. Gum arabic solution (6%) 5.0 ccs. 2 N ammonia 5.0 ccs. 2 N citric acid 7.5 ccs. 2%N manganese chloride (MnC12) 9.0 ccs. Ammonium thiocyanate (16 grms.

per litre) 9.0 ccs. Methylated spirit 20.0 ccs. Mauve dye 5.0 ccs. 4% solution chrome alum 2.5 ccs. 25% solution lead nitrate 2.0 ccs. solution formalin 0.75 ccs.

tine emulsion. Asolution of lead nitrate was then added to the emulsion and also small proportions of methylated spirit, mauve dye, chrome alum and formalin were incorporated, the actual formula being as follows:

Gelatin 24 gms.

Water 200 ccs. 2 N citric acid 2.5 ccs. 2 N silver nitrate 10.0 ccs. Z A N manganese chloride (MnCl2) 11.0 {ccs. Gum arabic solution (6%) 7.5 ccs. 25% gold chloride (NaAuCh) 1.0' ccs. Ammonium thiocyanate solution (16 grms. per litre) 7.5 ccs. Methylated spirit 20. ccs. Mauve dye 3 00$. 4% solution chrome alum 2.5 ccs. 25% solution lead nitrate 2.0 ccs. 40% solution formalin 0.75 ccs.

Typical exposures for papers coated with emulsions according to the above two formula are respectively:-

(1) Mercury vapour lamp 10-20 secs.

500 watt /2 Watt lamp at 6 ins 30-50 secs. (2) Mercury vapour lamp 50-150 secs.

500 watt /2 watt lamp at 6 ins 2-4 mins.

Conveniently the following procedure may be followed in developing the print. After exposure (Which-may in some cases be just sufficient to show the outlines of an image) the paper is washed for one minute and then transferred to a developer of the formula:-

It may be here noted that the developer should not contain any substantial proportion of sodium sulphite since this may have a detrimental action on the subsequent toning operation. Using a 24 gms;

developer of the above kind, development should be complete in about two to three minutes. Thereafter the print is immersed in an acid stop bath (e. g. a one per cent solution of hydrochloric, acid) 7 for one minute, then washed for two minutes, and finally transferred to the toning and fixing bath; The toning bath may conveniently comprise a 30% solution of sodium thiosulphate to which may, if desired, be added a small proportion of ammonium thiocyanate.

' Immersion in the toning and fixing bath is continued until the desired shade of colour has been reached, and the print is then withdrawn and washed thoroughly before drying.

Instead of fixing the print in a sodium thiosulphate solution it may, if desired, be toned after removal from the developing bath by placing it in a solution of common salt and potash alum until the colour has reached the desired tone, the print then being removed and fixed in thiosulphate in the ordinary way.

It will be appreciated that in the original preparation of the emulsion various modifications may be made without departing from the scope of the invention. For example instead of incorporating the manganese salt by using a chloride of manganese to precipitatethe insoluble silver chloride, another chloride precipitating solution may be employed and the manganese salt added separately.

The invention includes the manufacture of the emulsion as. described herein, paper and other material coated with that emulsion, and the special method for the production of the print. It will be appreciated that although the invention is particularly concerned with the preparation of a printing paper, other supports for the emulsion may be employed.

We claim: 4

1. A photographic paper or other support bearing a print-out emulsion comprising a silver salt content which is substantially insoluble in water, a soluble salt of manganese, and a gold salt.

2. A photographic paper or other support bearing a print-out emulsion comprising a silver salt content which is substantially insoluble in water, a soluble salt of manganese and a lead salt.

3. A photographic paper or other support bearing a print-out emulsion comprising a silver salt content which is substantially insoluble in water, a soluble salt of manganese and a thiocyanate.

4. A photographic paper or other support bear ing a print-out emulsion comprising a silver salt content'which is substantially insoluble in Water, a soluble'salt of manganese, a gold salt, a lead salt and a thiocyanate of an alkali metal or ammonium.

5. A method of preparing a print-out emulsion which comprises the precipitation of silver chloride from a solution of a soluble silver salt by the addition of a solution of manganese chloride.

' 6. A photographicpaper or other support bearing a print-out emulsion which has a silver salt content substantially insoluble in water, which contains self-toning ingredients and in which the print-out properties are produced by a content of a soluble manganese salt.

'7. A photographic paper or other support bearing a print-out emulsion which has a silver salt content consisting mainly of silver chloride, which contains .self-toning ingredients and in which the print-out properties are produced by a. content of a soluble manganous salt.

Cir

8. A photographic paper or other support bearing a print-out emulsion which has a silver salt content substantially insoluble in water, which contains self-toning ingredients and in which the print-out properties are produced by a content of manganous chloride.

9. A photographic paper or other support hearing a print-out emulsion which has a silver salt content substantially insoluble in water in the sense that when the emulsion is coated on paper the silver salt content will not percolate into the paper base, which emulsion contains self-toning ingredients and in which emulsion the printout properties are produced by the addition of a 5 soluble manganous salt.

WILLIAM AMBLER BERRY. BERTRAM VINCENT STORE. 

